Pipe elements, which include any pipe-like item such as pipe stock, as well as fittings, including, for example elbows, tees and straights and components such as valves, strainers, end caps and pump intakes and outlets, may be sealingly joined in end to end relation using mechanical pipe couplings, an example of which is disclosed in U.S. Pat. No. 7,086,131. The couplings are formed of two or more segments joined end to end by threaded fasteners. In use, the coupling segments are positioned surrounding the pipe elements and are drawn toward one another and into engagement with the pipe elements by tightening the threaded fasteners. The pipe elements may have circumferential grooves which are engaged by radially projecting keys on the pipe couplings to provide positive restraint to thrust loads experienced by the pipe elements when under internal pressure from the fluid within. An elastomeric gasket, often in the form of a ring, is positioned between the coupling segments and the pipe elements to ensure fluid tightness of the joint. The gasket may have glands which use the internal fluid pressure within the pipe elements to increase the maximum pressure at which it remains effective to prevent leaks. The gasket is compressed radially between the coupling segments and the pipe elements to effect the fluid tight seal desired.
To form a fluid tight joint using a mechanical coupling with grooved pipe elements it is necessary to control the dimensions of the circumferential grooves of the pipe elements so that the grooves properly engage the keys of the coupling elements and also allow the segments to move toward one another and compress the gasket sufficiently to effect the fluid tight seal. Grooves may be formed by cold working the side wall of the pipe element between opposed rollers which are forced toward one another to displace material of the pipe element, typically by hydraulic means, while they are turning about substantially parallel axes of rotation. The pipe element rotates in response (or the rollers orbit around the pipe circumference) and the groove is formed about the pipe element circumference. Dimensional control of the grooves is made difficult by the allowable tolerances of the pipe dimensions. For example, for steel pipe, the tolerances on the diameter may be as great as +/−1%, the wall thickness tolerance is −12.5% with no fixed upper limit, and the out of roundness tolerance is +/−1%. These relatively large dimensional tolerances present challenges when forming the circumferential grooves by cold working. It would be advantageous to develop a method and an apparatus which actively measures a parameter, such as the groove diameter, and uses such measurements, as the groove is being formed, to control the motion of groove forming rollers as they form the groove. This will avoid the trial groove and measure/adjust procedure of the prior art.